The present invention relates to a type of composite material which includes fiber material as a reinforcing material embedded in a mass of matrix metal, and more particularly relates to such a type of composite material in which the reinforcing material is a mineral fiber material and the matrix metal is aluminum, magnesium, copper, zinc, lead, tin, or an alloy having one or more of these as principal component or components.
In the prior art, various composite materials including fiber materials of various kinds as reinforcing material have been proposed. The advantages of such fiber reinforced materials include improved lightness, improved strength, enhanced wear characteristics, improved resistance to head and burning, and so on. In particular, for the fiber reinforcing material, there have been proposed the following kinds of inorganic fiber materials: alumina fiber, alumina-silica fiber, crystallized glass fiber, silicon carbide fiber, and silicon nitride fiber; and of the matrix metal aluminum alloy and various other alloys have been suggested. Such prior art composite materials are disclosed, for example, in Japanese Patent Laying Open Publication Nos. Sho 58-93948 (1983), Sho 58-93837 (1983), Sho 58-93841 (1983), and Sho 59-70736 (1984), of all of which Japanese patent applications the applicant was the same entity as the assignee of the present patent application, and none of which is it intended hereby to admit as prior art to the present application except insofar as otherwise obliged by law.
Inorganic fibers of the types mentioned above, however, are very much harder than the aluminum alloy or the like which is the matrix metal also mentioned above, and accordingly in the case of using these as the reinforcing fibers for a composite material there arise the problems that processing such as machining or the like is extremely difficult, and also that the amount of wear on cooperating parts which are in frictional contact with a part made of such composite material and slide thereagainst tends to be large. Further, inorganic fibers of the types described above are very expensive, and this makes the cost of composite materials including them very high. This cost problem, in fact, is one of the biggest current obstacles to the practical application of composite materials for making many types of actual components. Further, with these types of inorganic fibers used as reinforcing fiber material, the problem tends to arise, during manufacture of the composite material, either that the wettability of the reinforcing fibers with respect to the molten matrix metal is poor, or alternatively, when the reinforcing fibers are well wetted by the molten matrix metal, that a reaction between them tends to deteriorate the reinforcing fibers.
On the other hand, in contrast to the above mentioned inorganic materials, mineral fibers whose principal components are SiO.sub.2, CaO, and Al.sub.2 O.sub.3 are very inexpensive, and therefore if such fibers could satisfactorily be used as reinforcing fiber material for a composite material then the cost could be very much reduced. Further, the wettability of such mineral fibers with respect to molten aluminum alloys and the molten phases of other suitable candidates for consideration as matrix metal materials is very good, and there is little possibility of any harmful reaction occurring between such mineral fibers and such likely matrix metals, so that, as compared with the case of using as reinforcing fiber material a material which has poor wettability with regard to the molten matrix metal, or the case of using a reinforcing fiber material which undergoes a deleterious reaction with the molten matrix metal, a composite material can be manufactured which has superior mechanical characteristics such as strength. However, such mineral fibers, by virtue of their method of manufacture which will be discussed later in this specification, contain as an admixture about 50% by weight of non fibrous particles of various sizes. Since these non fibrous particles have in general much bigger diameters than the mineral fibers themselves, and are extremely hard, problems arise such as that the processing such as machining of a composite material which includes these non fibrous particles is very difficult, excessive wear is produced on cooperating parts which are in frictional contact with and slide against a part made of such composite material, and the strength of the composite material is not sufficiently improved over the strength of the matrix metal material by itself.